According to established orthodontic techniques, it is well known that one is able to ligate an archwire to a bracket utilizing an elastic, elastomeric or metal ligature. In a twin edgewise orthodontic bracket, the elastic ligature is stretched around respective undercuts of gingival and occlusal tie wings so as to overlay the archwire at mesial and distal ends of the bracket.
The ligating procedure involves carefully stretching the elastic or elastomeric ligature (or wrapping and twisting a metal ligature) around the tie wings utilizing appropriate orthodontic instruments. It has been found that the time-consuming ligation procedure contributes to lengthy chair time. Furthermore, the elastic ligatures are known to lose their elasticity with time and are subject to degradation. Also, the elastic and metal ligatures have been known to trap food particles in areas of the bracket which are difficult for the patient to clean, and to increase the level of friction against the archwire. Finally, the use of sharp metal ligatures around the bracket can subject the clinician to unnecessary exposure to infectious bacteria, or viruses such as hepatitis B, or possibly the HIV virus particularly in blood.
In an effort to overcome these disadvantages of elastic ligatures, certain advances have been made in the area of pre-engaging orthodontic brackets. Each of U.S. Pat. Nos. 4,144,642; 4,248,588; 4,698,017; 3,772,787; 4,786,242; 4,559,012; 4,561,844; 4,655,708; 4,077,126; 4,419,078; 4,634,661; 4,197,642; and 4,712,999 illustrate one or more designs of pre-engaging brackets. These prior art devices overcome some of the disadvantages associated with elastic ligatures. For example, pre-engaging orthodontic brackets eliminate, or at least reduce, exposure of the clinician to sharp ligatures, thereby alleviating the problem of contracting harmful bacteria or viruses. In addition, pre-engaging orthodontic brackets permit continuous low deflection differential archwire contact separately for both round and rectangular archwires at at least two different levels of contact, which is not possible with degrading elastic, elastomeric or rigid, high deflection metal ligatures. However, most of the known prior art pre-engaging orthodontic brackets lack the reliability and the accessible ease of operability that most clinicians require. In addition, the majority of prior art pre-engaging orthodontic brackets are of a single design that have three or fewer tie wings.
It is therefore an object of the present invention to provide a novel twin pre-engaging orthodontic bracket which obviates or mitigates at least one of the above-identified disadvantages associated with prior art orthodontic brackets.